公元前139年，张骞负责与西域各国的外交事务。当时，汉朝已经和中亚、西亚等地建立了贸易和文化联系，但与西域地区的交流非常有限，因此汉朝希望通过派遣使者的方式加强与西域各国的关系，进一步拓展贸易和文化交流。为此，汉武帝任命张骞为使者，带领一支使团前往西域。

In 139 B.C., Zhang Qian was responsible for diplomatic affairs with various Western countries. At that time, the Han Dynasty had already established trade and cultural connections with Central Asia, Western Asia, and other regions. However, communication with the Western Regions was limited. Therefore, the Han Dynasty aimed to strengthen relations with Western countries by sending envoys, further expanding trade and cultural exchanges. To achieve this, Emperor Wu of Han appointed Zhang Qian as the envoy to lead a delegation to the Western Regions.

张骞带领的使团共有数百人，包括武士、翻译、军官、马夫和商人等，携带了大量的贡品和礼物，以及装备和口粮等必要物资。

Zhang Qian's delegation consisted of hundreds of people, including warriors, translators, military officers, horsemen, merchants, etc. They carried numerous tributes, gifts, equipment, and essential supplies such as provisions.

他们从长安出发，沿着丝绸之路一路向西，在经过了长途跋涉后，张骞和他的使团最终抵达了大宛国（今乌兹别克斯坦南部），这个国家被誉为是丝绸之路上最富有、最强大的国家之一。

Setting out from Chang'an, they traveled westward along the Silk Road. After a long journey, Zhang Qian and his delegation eventually reached the Dayuan at Fergana Valley (now in southern Uzbekistan), a region renowned as one of the wealthiest and most powerful along the Silk Road.

在大宛国，张骞向当地的君主献上了汉武帝的书信，并成功地与他们建立了友好关系。此外，张骞还从大宛国得知了许多西域地区的情况，对于中西文化交流和经济贸易的推进起到了极为重要的作用。

In Dayuan, Zhang Qian presented a letter from Emperor Wu to the local ruler, successfully establishing friendly relations with them. In addition, Zhang Qian learned many details about the Western Regions from Dayuan, playing a crucial role in promoting cultural and economic exchanges between East and West.